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    <title>Document</title>
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    <script>
        // 求1+2!+3!+...+20!的值
        var total = 0;
        for (var a = 1; a <= 20; a++) {
            var c = 1;
            for (var i = 1; i <= a; i++) {
                c *= i
            }
            total += c;
        }
        console.log(total);
    </script>
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